This disclosure relates to steering systems for vehicles that improve the stability of the vehicle. More specifically, this disclosure relates to an active front steering actuator and a method for controlling a vehicle.
Motor vehicles, such as cars and trucks, require a steering system to control the direction of travel of the vehicle. The steering system controls the direction of travel of the vehicle through the control of one or more sets of road wheels. Such steering systems commonly transmit a driver""s intent from a steering wheel to the road wheels via a mechanical steering linkage. Thus, movement of the steering wheel by the driver causes a corresponding movement of the road wheels. Hydraulic and/or electric motor assisting systems are commonly used in combination with such mechanical systems. These assisting systems reduce the driver effort necessary to actuate the mechanical system.
One example of a hydraulically assisted mechanical system is provided in U.S. Pat. No. 4,009,641. Here, a hydraulically assisted steering gear is provided. Another example of a hydraulically assisted steering gear is provided in U.S. Pat. No. 5,341,701. The content of each are incorporated herein in their entirety by reference thereto.
In addition to merely controlling the direction of travel of the vehicle, it is desired for the steering system to improve the stability of the vehicle.
Accordingly, continued improvements in stabilizing the control of the vehicle through the steering system are desired.
A steering actuator comprising an intermediate shaft, an electric motor, a transmission, a first stopping device, a second stopping device, and a controller is provided. The steering column transmits a first rotational force to the intermediate shaft. The electric motor generates a second rotational force on a rotor shaft upon application of an electric current. The transmission transmits either or both of the first rotational force and the second rotational force to a lower shaft of a steering gear. The first stopping device prevents the first rotational force from being transmitted to the rotor shaft. Similarly, the second stopping device prevents the second rotational force from being transmitted to the steering column. The controller operates the steering actuator in a first mode, a second mode, or a third mode by selectively applying the electric current to the electric motor and the stopping devices.
A method of controlling a set of road wheels of a vehicle is provided. The method comprises detecting a current yaw force of the vehicle; comparing the current yaw force to a predetermined yaw force limit; converting only a first rotational force from a steering column to a first degree of change of the road wheels if the current yaw force is not above the predetermined yaw force limit; and converting only a second rotational force from a source other than the steering column to a second degree of change of the road wheels if the current yaw force is above the predetermined yaw force limit. The second degree of change introduces a steering induced yaw force to the vehicle to cancel at least a portion of the current yaw force.
The above-described and other features are appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.